From colloidal-silica sols to aerogels and xerogels

Abstract-By destabilization of quasi-monodisperse silica sols, fractal clusters can be obtained. Solvent evacuation gives a porous solid with fractal structure. Structural investigations of these colloidal aerogels by small-angle neutron scattering are presented, and compared to similar observations in concentrated sols and xerogels. An investigation of the vibrational modes of these materials by inelastic neutron scattering gives clear evidence of a strong non-Debye contribution in the low-frequency regime. Introduction. Silica gels and aerogels are known to be excellent model-materials for the study of fractal inhomogeneous media [I]. They can be prepared under various physical and chemical conditions leading to strongly different microstructures. Small-angle scattering techniques using neutrons or X-rays have proven to b